AU2004235642A1 - A High Power Factor DC to DC Converter - Google Patents

Description

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BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a DC-to-DC converter with power factor correction.

Description of the Prior Art.

Traditional power supplies with a simple diode rectifier draw highly nonlinear current that pollutes the utility or power circuit. In order to reduce the current harmonics and meet the requirement of the regulation EN61000-3-2, many approaches have been proposed. Active twostage power factor correction (PFC) and single-stage PFC, active power filters are typical ways to reduce the harmonics and improve the power factor. The two-stage PFC is well known, it uses an inductor and a switch to boost the voltage across the filter capacitor to prevent that AC power source directly charges filter capacitor. This topology uses special IC and has some shortcomings: one of those is that it increases the voltage across the converter switch and this will increase the risk of damage to the switch and it also increases the power loss. The other is that the special IC's function could result in inrush current.

Brief Summary of the Invention Therefore, the inventor has come up with the present invent whereby the operation of the DC to DC converter and operation of power factor correction will complete at the same time.

The primary objective of the invention is to provide a high power factor DC to. DC converter without increasing risk of the damage to the switch.

The second objective of the invention is to provide a high power factor DC to DC converter with less power loss.

The third objective of the invention is to provide a high power factor DC to DC converter with less cost circuit.

The four objective of the invention is to provide a mechanism to protect converter from current over shooting and voltage over shooting.

The invention is a high power factor DC to DC converter. It uses new topology to realize the high power factor DC to DC conversion.

It uses capacitors and a diode to clamp voltage across the main switch to certain level. This decreases the risk of the damage to the main switch and at the same time to prevent the power loss in the switching operation. It uses the transformer that has some leaking inductor to prevent circuit from large current failure. It uses common PWM IC and less expensive switching component to reduce the cost.

The invention relates to the circuit diagram as Fig.2 for high PFC DC to DC converter is comprised: The rectifier R, its input coupled to the AC source and its output, the positive output coupled to diode DIand Cl and the negative output coupled to C1, C2, C4, D2 and the main switch Q2.

The diode DI, its anode coupled to the positive output of the rectifier R and its cathode coupled to primary winding of the transformer T.

The capacitor C1 coupled between the output of the rectifier R. The capacitor Cl and the diode D I is used to prevent power loss because low speed of rectifier.

SThe transformer T, its primary winding and the diode D1 connected in series with the anode of the diode D1 connected to the positive output of the rectifier R and the primary winding to main switch Q2. It transfers power from the primary circuit to secondary.

O The main switchQ2, connected between primary winding of the transformer T and the negative output of the rectifier R, serves power chopper.

The diode D5, its anode coupled to junction of the switch Q2 and the primary of the transformer T and its cathode coupled to the capacitor C2.

S The diode D2, its anode coupled to the negative output of the rectifier R and its cathode coupled to the negative end of the capacitor C3.

S The capacitor C3, its positive end coupled to the cathode of the diode D5 and its negative end coupled to the anode of the diode D3.

The diode D3, its anode coupled to the negative end of the capacitor C3 and its cathode coupled to the positive end of the capacitor.

The capacitor C4, its positive end coupled to the cathode of the diode D3 and its negative end coupled to the output of the rectifier R The diode D4, its cathode coupled to cathode of the diode D5 and its anode coupled to the positive end of the capacitor C4.

The diode D2, D3, D4, capacitor C3 and C4 consist of a valley fill circuit that provides the power to converter when the input voltage is lower than a certain level. This circuit is connected in parallel with the capacitor C2.

The capacitor C2, coupled to junction of the switch Q1 and the cathode of the diode D2 and its other end coupled to the negative output of the rectifier R. It serves as compensating input current to sine waveform and at the same time preventing power loss during switching.

The auxiliary switch QI, coupled to positive end of the capacitor C2 and coupled junction of the cathode of the diode D1 and the primary of the transformer, serves as discharging current from the capacitor C2.

The secondary circuit can be constructed one output voltage or minulti-output voltage circuit.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an Active two-stage power factor correction circuit.

Fig.2 is a present invention PFC circuit Fig 3 is another diagram of the present invention.

Detailed Description of Current Invention.

The embodiments of the present invention will be described bellow with reference to the drawings.

Fig.2 describes a constitution of a DC power supply device of an embodiment of the present invention. The AC power source line is coupled to the input of the rectifier R. The anode of diode D1 is couple to the positive output of the rectifier R. The primary winding of the transformer T and diode D1 connected in series with the other primary winding of the transformer T connected to drain of MOSFET Q2 and the anode of the diode D1 to the rectifier R. The source of MOSFET Q2 is connected to the negative output of the rectifier R. The anode of the diode D5 is coupled to the junction of the primary winding of the transformer T and the drain of switch MOSFET Q2. The cathode of the diode D5 is coupled to the auxiliary switch MOSFET QI and the capacitor C2. The auxiliary switch MOSFET Q1 is the capacitor C2 and the source of the auxiliary switch MOSFET Q1 is coupled to cathode of the diode D1. The other end of capacitor C2 is connected to the negative output of the rectifier R. The capacitor C3, C4, diode D2, D3, and D4 consist of a valley fill circuit that connected parallel with the capacitor C2.

The capacitor C2 and the valley fill circuit are used to clamp the voltage to certain level and the valley fill circuit also discharge the store energy during lower input voltage at the AC circle.

Fig 3 is the circuit that uses inductor to boost voltage of the valley fill circuit The operation of present invention system is as follow: At begin the AC power through the rectifier R and the primary winding of the transformer T and diode Dl, D5 charges the capacitor C2, C3 and C4. After the capacitors are charged to maximum 1 voltage level of the rectified AC voltage, the AC power cannot charge capacitors C3 and C4 without the voltage induced in the primary winding of the transformer. One cycle operation of the system is: at stage 1, the auxiliary switch Q1 and main switch Q2 are on, the current discharges from the capacitor C2 through the auxiliary switch Q1, the primary winding of the S transformer T and the main switch Q2. At this stage in the secondary winding of the transformer T induces a voltage that charges the capacitors in secondary circuit. At stage 2, when the voltage of the capacitor C2 is lower than input rectified voltage, the current is drawn from the AC power line conducts through the rectifier R, the diode DI, the primary winding of the transformer T and the main switch Q2. (When the voltage of the capacitor C2 and of the input rectified AC voltage are lower than the voltage across the capacitor C3 or C4. The current, drawn from the capacitors C3 and C4, conducts through the rectifier R, the diode DI, the primary winding of the transformer T and the main switch Q2.) At the stage 3, the auxiliary switch Q1 and main switch are off and the current drawn from the AC power source conducts through the rectifier R, the primary winding of the transformer T and the diode D5, charges the capacitor C2. When the voltage in transformer T plus the input rectified voltage is higher than the voltage across the capacitor C3 plus the voltage across capacitor C4 the current drawn from the AC power line charges the capacitor C3 and C4. At this stage in the secondary winding circuit there is current charging capacitors in secondary circuit. The next sequence repeats above the operation. Every cycle there is current that charges the capacitor C2 and the capacitors C3 and C4. When rectified AC voltage is high, there is more current drawn from the AC power line, when rectified AC voltage is low, there is less current drawn from the AC power line, Therefore the present invention power factor is near 1. The capacitor C2 functions to compensate the input current waveform to a sine waveform and to prevent the power loss during main switch Q2 switching off, the capacitor C2 is selected according to the converter power rating. The capacitors C3 and C4 function to provide power to converter when the input rectified AC voltage is lower than the voltage across capacitor C3 and C4 and they also function to clamp the voltage across the main switch during switching off to certain level. The capacitor C2 and capacitors C3, and C4 are used to protect main switch Q2 from the voltage over shooting during switching off and it make the converter more reliable than the traditional two-stage PFC converter. The transformer in this application required some leaking inductance to provide a mechanism to protect the main switch Q2 from current over shooting. When the input rectified DC voltage level is high, the rectified DC power provides more power to secondary and charges the capacitor C2 and capacitor C3 and C4. In the some stage the power charged and power discharged from the capacitor C2 and capacitors C3 and C4 are equal, the power transform to the secondary is provided by input AC power. When the input rectified DC voltage is very low, the power transferred to the secondary circuit is provided by capacitor C3 and C4. The voltage across the capacitor C3 and C4 keeps stable. For better power factor and waveform and output voltage stable, it requires voltage across the capacitor across C3 or C4 above 210 v for 240 AC power. By arrangement of the PFM pulse or PWM Pulse, the system has a consistent DC output. This converter can be configured for single output or multi-output power supply.

An example of the above circuit (Fig.2) is a 120w PFC DC to DC converter and its output is a S multi-output: 12V: 3A; 5V: 11A; 3V: 11A. It uses the MOSFET IRF450 as the main switch, the MOSFET IRF840 as the auxiliary switch.

An example of the circuit (Fig.3) is a 120w PFC DC TO DC converter. Its output is multi-output: 12V: 4A; 5V: 10A; 3V: 10A. It uses the MOSFET IRF450 as main switch, the MOSFET IRF840 as auxiliary switch and inductor is ImH, The PMW control IC is KA3845.

Claims (7)

1. A PFC DC-to-DC converter comprising: A rectifier bridge having an input, coupled to said AC source, and an output. A first diode said with its anode connected to the positive output of the rectifier and its cathode connected to the primary winding of the transformer. A transformer said primary winding connected between said cathode of the first diode and said the second switch. A second switch said connected between the primary of the transformer and negative output of the rectifier. f A second capacitor said connected between negative output of the rectifier and the first M switch. tA second diode said its anode coupled to the negative output of the rectifier and its cathode Oconnected to the negative of the third capacitor. A third diode said its anode coupled to the negative end of third capacitor and its cathode coupled to the positive end of the fourth capacitor. A fourth diode said its anode coupled to the positive end of the fourth capacitor and its cathode coupled to the second capacitor. A fifth diode said its anode coupled to the junction of primary winding of the transformer and the second switch and its cathode coupled to the second capacitor. A third capacitor said its positive end coupled to the second capacitor and its cathode to the anode of the third diode. A fourth capacitor said its positive end coupled the cathode of the third diode and its negative end to the negative output of the rectifier. A first switch said connected between the cathode of the second the diode and the cathode of the first diode. A secondary circuit said outputs a single voltage or multi-voltage.

2. The DC-to-DC converter of claim 1 said where the transformer has some leakage inductance.

3. The DC-to-DC converter of claim 1 said where the fifth diode, the second capacitor, valley fill circuit, the third capacitor, the fourth capacitor, the second diode, the third diode, fourth diode, are used to be as a circuit, to clamp voltage.

4. The DC-to-DC converter of claim 1 where said the first diode and the first capacitor are used to prevent power loss because the slow speed of rectifier. The DC-to-DC converter of claim 1 said where the second capacitor is used to correct the input current to a sine waveform.

Where said the valley fill circuit, the third capacitor, the fourth capacitor, the second diode, third diode and the four diode, is used to provide power to converter during lower input voltage period.

6. A PFC DC-to-DC converter comprising: A rectifier bridge having an input, coupled to said AC source, and an output. A first diode said with its anode connected to the positive output of the rectifier and its cathode connected to the primary winding of the transformer. A transformer said primary winding connected between said cathode of the first diode and said the second switch. A second switch said connected between the primary of the transformer and negative output of the rectifier. A second capacitor said connected between negative output of the rectifier and the first switch. A second diode said its anode coupled to the negative output of the rectifier and its cathode connected to the negative of the third capacitor. A third diode said its anode coupled to the negative end of third capacitor and its cathode coupled to the positive end of the fourth capacitor. N A fourth diode said its anode coupled to the positive end of the fourth capacitor and its cathode coupled to the second capacitor. A fifth diode said its anode coupled to the junction of primary winding of the transformer and the second switch and its cathode coupled to the second capacitor. A third capacitor said its positive end coupled to the second capacitor and its cathode to the anode of the third diode. A fourth capacitor said its positive end coupled the cathode of the third diode and its negative end to the negative output of the rectifier. OA sixth diode said its anode connected to the positive output of the rectifier and its cathode connected to the inductor. An inductor said its one end connected to the cathode of the sixth diode and its other connected to the second switch. A first switch said connected between the cathode of the second the diode and the cathode of the first diode. A secondary circuit said outputs a single voltage or multi-voltage.

7. The DC-to-DC converter of claim 6 said an auxiliary circuit comprising of an inductor, the sixth diode to boost the voltage across the third capacitor and the fourth capacitor.